• 마이크로전자및패키징학회지
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• 제9권3호
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• pp.37-41
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• 2002

본 연구에서는 자기 공명 특성을 이용한 박막 센서의 멤브레인 및 박막 센서의 특성을 알아보았다. 멤브레인으로 유망한 물질로 $Si_xN_y$과 SiC가 있으며, 최적의 멤브레인 형성 조건을 알고자 박막의 잔류 응력 및 물성을 비교 분석하였다. 그 중에서 박막 센서에 적용 가능한 멤브레인으로 SiC보다 적절한 인장응력과 낮은 열팽창 계수를 가지는 $Si_xN_y$이 센서의 구조층으로 우수하였으며, $Si_xN_y$위에 박막 센서 물질을 증착 및 패턴닝(patterning)을 함으로써 센서의 자기 이력 곡선 및 자기 공진 주파수를 분석하였다. 센서에 인가되는 외부 자기장을 제거하면 자장에 의해 형성된 자화(magnetization)가 탄성 모드로 바뀌면서 에너지 방출에 의해 센서에서 전압이 발생하는데 이때 전압 발생 구간이 길어지면 기계적 진동이 야기되어 신호가 발생한다. 그리고 센서의 길이 및 폭이 증가할수록 자기공명 주파수가 감소하는 것을 볼 수 있다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 추계학술대회논문집
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• pp.330-335
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• 2000

This paper deals with sensing ability of smart sensor that has a sensing ability of distinguish materials. We have developed new signal processing method that have distinguish different materials. We made the two type of smart sensors for experiment. The first type of smart sensor is H2 type. The second type of smart sensor is HH type. The smart sensor was developed for recognition of material. And then we developed estimation method of sensing ability of smart sensors. The first method(Sensing Ability Index) is developed for H2 smart sensor. The second method($R_{SAI}$ Index) is developed for HH smart sensor. We estimated sensing ability of smart sensor with new SAI and $R_{SAI}$ method. This paper describes our primary study for a new method of estimate sensing ability of smart sensor, which is need for precision work system. This is a study of dynamic characteristics of smart sensor according to frequency and displacement changing with new SAI and $R_{SAI}$ method. Experiment and analysis are executed for proper dynamic sensing condition. First, we developed advanced smart sensors. Second, we develop new SAI and $R_{SAI}$ methods that have a sensing ability of distinguish materials. Dynamic characteristics of smart sensor are evaluated through new SAI and $R_{SAI}$ method relatively. We can use the new SAI and $R_{SAI}$ method for finding materials. Applications of this method are finding abnormal condition of object(auto-manufacturing), feeling of object(medical product), robotics, safety diagnosis of structure, etc.

• Smart Structures and Systems
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• 제11권6호
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• pp.589-604
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• 2013

Identification of damage has become an evolving area of research over the last few decades with increasing the need of online health monitoring of the large structures. The visual damage detection can be impractical, expensive and ineffective in case of large structures, e.g., offshore platforms, offshore pipelines, multi-storied buildings and bridges. Damage in a system causes a change in the dynamic properties of the system. The structural damage is typically a local phenomenon, which tends to be captured by higher frequency signals. Most of vibration-based damage detection methods require modal properties that are obtained from measured signals through the system identification techniques. However, the modal properties such as natural frequencies and mode shapes are not such good sensitive indication of structural damage. Identification of damaged jacket type offshore platform members, based on wavelet packet transform is presented in this paper. The jacket platform is excited by simple wave load. Response of actual jacket needs to be measured. Dynamic signals are measured by finite element analysis result. It is assumed that this is actual response of the platform measured in the field. The dynamic signals first decomposed into wavelet packet components. Then eliminating some of the component signals (eliminate approximation component of wavelet packet decomposition), component energies of remained signal (detail components) are calculated and used for damage assessment. This method is called Detail Signal Energy Rate Index (DSERI). The results show that reduced wavelet packet component energies are good candidate indices which are sensitive to structural damage. These component energies can be used for damage assessment including identifying damage occurrence and are applicable for finding damages' location.

• 대한조선학회논문집
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• 제55권1호
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• pp.37-44
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• 2018

To understand the dynamic characteristics of the vessel with hydroelastic response, it is very important to estimate the dynamic modal parameters such as mode shapes, natural frequency, and damping ratio. These dynamic modal parameters of full scale ship are a priori unknowns, hence to be estimated directly based upon the full scale measurement data. In this paper, dynamic modal parameters were extracted by signal processing of acceleration and strain data measured from a large container ship whose loading capacity is 9400TEU. The mode shapes of the vibrating hull were identified using the proper orthogonal decomposition and the vibration response of hull was decomposed into its modal magnitudes. Natural frequencies of specific modes were derived via Fourier transform of these modal magnitude. Also, the free decay signal of the vibrating hull was obtained through the random decrement technique and the damping ratio was estimated with accuracy.

• 융합신호처리학회논문지
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• 제10권1호
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• pp.86-92
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• 2009

유도 전동기의 사용이 증가함에 따라 유도전동기의 고장은 산업 사회에 커다란 피해를 끼치게 되었다. 그렇기 때문에 유도 전동기의 고장을 찾아내는 것은 매우 중요한 문제로 부각되었다. 하지만 그 중에서도 문제점은 유도전동기의 고장은 종종 오랜 시간에 걸쳐 진행된다는 것이다. 그것은 빠른 진단이 매우 중요하다는 것을 뜻한다. 이에 대해 많은 연구가 진행되어 왔으며 가장 일반적으로 쓰이는 고장 진단 방법은 진동 센서를 이용한 전동기의 기계적 고장을 찾는 방법이다. 하지만 이 방법은 신뢰도가 높은 검증 방법임에도 불구하고 높은 시스템 가격과 활용의 어려움으로 인해 새로운 방법들이 시도가 되었다. 이 논문은 시스템을 기반으로 웨이블릿 변환을 이용한 유도전동기의 고장 진단 기술을 구현하는 것을 보여주며 윈도우즈 기반 C++을 이용하여 고장인지 아닌지를 결정하는 알고리즘으로 구성되어 있다. 전체 시스템은 전류 데이터 수집 보드와 PC를 이용한 신경망 알고리즘으로 실시간으로 수행 될 것이다.

• 한국구조물진단유지관리공학회 논문집
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• 제22권1호
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• pp.48-55
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• 2018

본 연구의 목적은 구조 시스템의 구조적 손상에 의한 고유주파수 감소율과 감쇠변수 증가율을 비교 분석하는 것이다. 이를 위하여 저주파 영역의 고유주파수와 비교적 높은 감쇠변수 특성을 갖는 2경간 H-Beam을 대상으로 실내실험과 수치해석을 수행하였으며, 충격하중에 대한 손상 전과 손상 후 응답신호를 각각 14개 위치에서 분석하였다. 각 위치에 대한 손상 전과 손상 후 응답신호는 푸리에 변환을 통하여 고유주파수 감소율을 분석하였으며, 감쇠변수 증가율은 웨이블릿 변환을 통하여 수행되었다. 웨이블릿 변환은 최대 웨이블릿 계수에 대응되는 스케일의 시간함수 분리가 가능하기 때문에 감쇠변수 평가에 대한 정확성을 높일 수 있다. 손상 전과 손상 후 계측된 응답신호에 대하여 고유주파수 감소율은 민감하지 못한 결과로 평가되었고, 감쇠변수 증가율은 비교적 큰 변화량을 보여 구조 시스템의 손상도 평가에 신뢰할 수 있는 결과를 보여주었다.

• International Journal of Computer Science & Network Security
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• 제22권2호
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• pp.123-130
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• 2022

During the past decades, detection of gear defects remains as a major problem, especially when the gears are subject to non-stationary phenomena. The idea of this paper is to mixture a multilevel wavelet transform with a fast EMD decomposition in order to early detect gear defects. The sensitivity of a kurtosis is used as an indicator of gears defect burn. When the gear is damaged, the appearance of a crack on the gear tooth disrupts the signal. This is due to the presence of periodic pulses. Nevertheless, the existence of background noise induced by the random excitation can have an impact on the values of these temporal indicators. The denoising of these signals by multilevel wavelet transform improves the sensitivity of these indicators and increases the reliability of the investigation. Finally, a defect diagnosis result can be obtained after the fast transformation of the EMD. The proposed approach consists in applying a multi-resolution wavelet analysis with variable decomposition levels related to the severity of gear faults, then a fast EMD is used to early detect faults. The proposed mixed methods are evaluated on vibratory signals from the test bench, CETIM. The obtained results have shown the occurrence of a teeth defect on gear on the 5th and 8th day. This result agrees with the report of the appraisal made on this gear system.

• 한국정밀공학회지
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• 제22권8호
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• pp.143-150
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• 2005

To verify applicability of multi-dimensional spectral analysis (MDSA) fur noise source identification two different approaches which are frequency response and coherent function have been investigated. The coherence function approach appears able to separate the correlated system when the noise sources were coherent. In this study, we identify contribution of structure-borne-noise of vehicle HVAC system using MDSA method. Firstly, to identify the applicability of MDSA method, 4-inputs of vehicle HVAC system were the signals measured by accelerometers attached on the selected noise sources which were composed of blower, evaporator, heater and duct. While 1-output which was driver's position sound was the SPL signals measured by a remote microphone, when the blower motor was operating. We identify efficiency of systems modeled with four Inputs/single output through ordinary coherence function (OCF) and partial coherence function (PCF). As a result of experiment, the blower accounted for $62-88\%$ of the overall level of sound energy density. Also, according to the analysis of acoustic signal and vibration signals measurement, an investigation of the noise source identification in the vehicle HVAC is presented. With the sound intensity method, the major sources of the vehicle HVAC radiation are verified. Also the method of improving the noise reduction is proposed by attaching damping patch access to blower motor and noise reduction is verified.

• 대한기계학회논문집A
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• 제29권12권
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• pp.1653-1659
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• 2005

In this study, the performance of a DPRMs is evaluated and the measurement precision for the pile driving is presented. The DPRMs is a visual-measurement system for the pile rebound and the penetration movement using a high speed line-scan camera. The DPRMs generates the measurement deviation. It is caused by the strong impact for the pile driving. To reduce it, the vibration signal analysis about the pile driving is performed. As a result, it is confirmed that the tilting frequency of a camera-tripod structure corresponding to excitation frequency range of the ground is under 40Hz. Through the structure modification, the camera-tripod structure is redesigned to the model being free itself from the excitation frequency range of the ground. By the verification testing about the improvement effects, it is inspected that the tilting and measurement deviation of the redesigned DPRMs are reduced.

• 한국산학기술학회논문지
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• 제11권9호
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• pp.3435-3440
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• 2010

표면탄성파를 이용한 RF소자의 성능을 단순히 작동 유무로만 평가할 수 있는 전기적인 성능 평가방법과 달리 위치에 따른 표면탄성파의 형성 정도를 실시간으로 검사할 수 있는 광학적 방법을 제시하였다. 광학적 방법을 이용한 표면 탄성파의 측정 조건과 한계를 제시하였고 간섭 및 회절 현상을 이용하여 RF신호의 입력 유무에 따른 광학적 해석을 하였다. 단일 모드 레이저를 이용하여 중심 주파수가 105MHz인 중계기 필터의 동작을 실험적으로 측정하고 이론적으로 분석하였다. 본 논문에서는 다기능 서비스를 제공하는 복합 주파수 RF 모듈의 고품질화를 위한 방법으로 표면탄성파의 에너지 분포를 시각화하고 실시간으로 평가할 수 있는 광학적 방법을 제시하였다.